The article compares two methods of determination of the particle size distribution of fine ash. The respective methods compared are the sieve analysis and laser difraction. The former is one of the oldest methods in use, applicable to size separation of large grain size particles. The latter is a modern advanced method that employs lase diffraction to determine the size distribution. For the measurement itself, the sieve analyser Analysette 3 PRO and the universal laser diffraction device Analysette 22 MicroTec plus, both from the Fritsch company, were applied. The comparison was made by analysing fine ash particles from biomass burners. The particles were in the size range of 0.08 μm to 2000 μm. and Obsahuje seznam literatury